1. Field of the Invention.
This invention relates generally to metal foundry articles and, more specifically, to improvements for riser linings in metal foundry castings.
2. Description of the Prior Art.
The manufacture of cast metal articles in foundries is well known in the art. Typically, one pours molten metal into a two-part mold where the metal gradually cools and hardens. Because molten metal shrinks during the cooling process, it is necessary to provide a reservoir of molten metal to flow into the shrinkage voids in the casting as the metal cools. The reservoirs of molten metals are known as risers. The concepts of risers in molds is well known in the art. The concepts of different types of riser liners are well known in the art. An example of a typical riser liner is shown in the Washburn U.S. Pat. No. 900,970. Washburn shows a one-piece riser liner made out of clay and suggests that the riser liner could be made of asbestos, wood or metal. A type of restriction device for use in sand castings is shown in Nieman U.S. Pat. No. 3,831,662. Nieman shows a frangible member located between the cope and the drag of the castings but not as part of a riser liner. The frangible member allows flow of metal therethrough as well as to facilitate clean removal of the solidified metal in the riser liner. The structure in the Nieman U.S. Pat. No. 3,831,662 comprises a frangible thin wall member made from a ceramic material. Nieman's purpose of using a frangible thin wall member is for breaking the solidified metal in the riser free from the casting after solidification and for controlling the amount of metal flowing into the mold.